using System;
using System.Collections.Concurrent;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Svrnty.CQRS.Events.Abstractions.Projections;

namespace Svrnty.CQRS.Events.Projections;

/// <summary>
/// In-memory implementation of projection checkpoint storage for development/testing.
/// </summary>
/// <remarks>
/// <para>
/// <strong>Warning:</strong> This is an in-memory store. All checkpoints are lost on restart.
/// For production, use PostgresProjectionCheckpointStore or another persistent implementation.
/// </para>
/// <para>
/// Thread-safe implementation using ConcurrentDictionary.
/// </para>
/// </remarks>
public sealed class InMemoryProjectionCheckpointStore : IProjectionCheckpointStore
{
    private readonly ConcurrentDictionary<string, ProjectionCheckpoint> _checkpoints = new();

    /// <inheritdoc />
    public Task<ProjectionCheckpoint?> GetCheckpointAsync(
        string projectionName,
        string streamName,
        CancellationToken cancellationToken = default)
    {
        var key = GetKey(projectionName, streamName);
        var checkpoint = _checkpoints.TryGetValue(key, out var value) ? value : null;
        return Task.FromResult(checkpoint);
    }

    /// <inheritdoc />
    public Task SaveCheckpointAsync(
        ProjectionCheckpoint checkpoint,
        CancellationToken cancellationToken = default)
    {
        if (checkpoint == null)
            throw new ArgumentNullException(nameof(checkpoint));

        var key = GetKey(checkpoint.ProjectionName, checkpoint.StreamName);
        _checkpoints[key] = checkpoint;
        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public Task ResetCheckpointAsync(
        string projectionName,
        string streamName,
        CancellationToken cancellationToken = default)
    {
        var key = GetKey(projectionName, streamName);
        _checkpoints.TryRemove(key, out _);
        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public Task<ProjectionCheckpoint[]> GetAllCheckpointsAsync(
        string projectionName,
        CancellationToken cancellationToken = default)
    {
        var checkpoints = _checkpoints.Values
            .Where(c => c.ProjectionName == projectionName)
            .ToArray();

        return Task.FromResult(checkpoints);
    }

    private static string GetKey(string projectionName, string streamName)
    {
        return $"{projectionName}::{streamName}";
    }
}